Cochlear implants and other inner ear prostheses are one option to help profoundly deaf or severely hearing impaired persons. Unlike conventional hearing aids that just apply an amplified and modified sound signal; a cochlear implant is based on direct electrical stimulation of the acoustic nerve. Typically, a cochlear implant stimulates neural structures in the inner ear electrically in such a way that hearing impressions most similar to normal hearing is obtained.
More particularly, a normal ear transmits sounds as shown in FIG. 1 through the outer ear 101 to the tympanic membrane (eardrum) 102, which moves the bones of the middle ear 103 (malleus, incus, and stapes) that vibrate the oval window and round window openings of the cochlea 104. The cochlea 104 is a long narrow duct wound spirally about its axis for approximately two and a half turns. It includes an upper channel known as the scala vestibuli and a lower channel known as the scala tympani, which are connected by the cochlear duct. The cochlea 104 forms an upright spiraling cone with a center called the modiolar where the spiral ganglion cells of the acoustic nerve 113 reside. In response to received sounds transmitted by the middle ear 103, the fluid-filled cochlea 104 functions as a transducer to generate electric pulses which are transmitted to the cochlear nerve 113, and ultimately to the brain.
Some persons have partial or full loss of normal sensorineural hearing. Cochlear implant systems have been developed to overcome this by directly stimulating the user's cochlea 104. A typical cochlear prosthesis may include two parts: the speech processor 111 and the implanted stimulator 108. The speech processor 111 typically includes a microphone, a power supply (batteries) for the overall system and a processor that is used to perform signal processing of the acoustic signal to extract the stimulation parameters. The speech processor may be a behind-the-ear (BTE-) device.
The stimulator 108 generates the stimulation patterns (based on the extracted audio information) that are sent through an electrode lead 109 to an implanted electrode array 110. Typically, this electrode array 110 includes multiple electrodes on its surface that provide selective stimulation of the cochlea 104. For example, each electrode of the cochlear implant is often stimulated with signals within an assigned frequency band based on the organization of the inner ear. The placement of each electrode within the cochlea is typically based on its assigned frequency band, with electrodes closer to the base of the cochlea generally corresponding to higher frequency bands.
The connection between speech processor and stimulator is usually established by means of a radio frequency (RF-) link. Note that via the RF-link both stimulation energy and stimulation information are conveyed. Typically, digital data transfer protocols employing bit rates of some hundreds of kBit/s are used.
A totally implantable cochlear implant (TICI) is a cochlear implant system without permanently used external components such as an external speech processor. The implantable TICI typically includes a microphone and subsequent stages perform audio signal processing for the implementation of a particular stimulation strategy (e.g., CIS). It also includes stimulation electrodes, power management electronics, and a coil for the transcutaneous transmission of RF signals.
Unlike a pacemaker implant, the power supply of a TICI generally cannot be established by means of a non-rechargeable battery. This is because the overall pulse repetition rate of a TICI is much higher. For example, typically about 20 kpulses/s are generated by a cochlear implant using CIS, as compared to about 1 pulse/s in a pacemaker. Besides, a cochlear implant typically performs complex audio signal processing, as compared to simple sensing tasks performed in a pacemaker. Consequently, a rechargeable battery is typically required in a TICI, which needs recharging after a particular time period of operation. To recharge the battery, an external device is often used for transcutaneous transmission of RF/power signals.
As shown in FIG. 2, an external part 201 includes a first magnet 205. A TICI 202 located under the skin 203 and embedded in bone 204 typically includes a second magnet 206 and a coil 208. The first magnet 205 is positioned over the second magnet 206 such that the external part 201 is held against the implant 202 in an optimum position. By maintaining such a position, an external coil 207 associated with external part 201 can, via inductive coupling, transmit power to the coil 208 of implant 202.
At various times, such as when sleeping or during an emergency, it may be desirable for the user to turn the TICI off for purposes of, without limitation, safety or power conservation. In addition to turning the TICI off, the capability to turn the TICI back on is often equally desirable. However, external control of the TICI is currently inhibited since the external component provides power, but not data/control information.